Cardinal Tetra Care (2026)

Species guide

Cardinal Tetra Care Guide (Planted Tank)

Fish

Cardinal tetras (Paracheirodon axelrodi) look like neons with more red. They are larger, more expensive, and pickier: soft acidic water, a real school (8–12+), and a planted 20-gal minimum. If you want the easy tetra, buy neons.

School 8–12+
20+ gal
Soft water
Not a neon

Quick facts

Temp	24–28 °C — slightly warmer than many neon tanks
pH / GH	pH 5.5–7.0, very soft–soft; avoid hard tap shock
Volume	20+ gal for a proper school
School	8–12+; six is the absolute floor
Length	~5 cm adult — bigger than P. innesi
Light	Dim–medium; plants + floating cover
Cycle	Fishless; never dump into a new tank
Lifespan	4–6+ years if water stays stable

Overview

Neon tetras (P. innesi) stay smaller and forgive more. Cardinals show a full red stripe to the tail and need more room. Same family, different care budget.

Cycle: fishless vs fish-in. Plants: Anubias · Java fern · Java moss · crypt. Community: corys · CPD · chili rasbora. Budget: first community · low-tech $150.

How to keep them

Step 1 Buy a school, not three show fish
Cardinals hide and fade in tiny groups. Eight is the real start; twelve looks like a river.
Step 2 Match tap or mix RO before they arrive
Hard alkaline tap + wild-type cardinals = shock. Test GH/KH. Drift slowly if you must remineralize.
Step 3 Plant cover + open midwater
Moss and fern on wood, crypts in the back, swim lane in the middle. Bright barren sand = pale fish.
Step 4 Feed small, varied meals
Micro pellets + occasional frozen. They will not thrive on one flake brand forever.
Step 5 Quarantine
Cardinals travel poorly. Ich after import is common. Do not seed a shrimp display.

Common problems

Faded colors, hanging at the back

Why: Too few fish or harsh light / hard water.

Fix: Increase school; add floaters; check GH.

Ich after adding to a planted tank

Why: Shipping stress + temp swing.

Fix: Stable heat; planted-safe treatment; quarantine next batch.

Dying one-by-one after a water change

Why: Tap parameter spike.

Fix: Smaller changes; condition; match temperature exactly.

Nipped fins

Why: Bad tank mates.

Fix: No tiger barbs, no male betta in the same 20-gal.

Tank mates

Excellent: corys on sand, otos in a mature tank, chili rasboras if the tank is 20+.
OK: cherry shrimp — adults usually ignore them; fry are snacks. See shrimp tank mates.
Skip: guppies if you want very soft water; bettas in the same nano; goldfish.
Do not mix ‘one neon + one cardinal’ as a fake school — they do not fill each other’s numbers.